This invention relates to the field of optical range mapping of the nontriangulation type.
In activities as diverse as midair refueling, automatic target recognition, robotic vision, space vehicle docking, industrial inspection and customized equipment design, for example, there is need for precise mappings of range measurements. Often such measurements are over distances in excess of that accommodated by conventional graduated tension member measurement or impractical of such measurement. The term mapping as used here includes range determination for a multiplicity of different points located on the distal target shape of the target object.
In the past such techniques as triangulation using optical images taken from two different viewpoints, or the time for energy propagation to and from a distal target object have been employed for accomplishing range measurements. In many range finding systems, however, there is need for speed and accuracy and operational simplicity in determining the range map of a distal target such as preclude the use of previous measurement techniques. The triangulation range mapper, for example, as is often used in cameras and in artillery measurement periscopes is slow and often cumbersome in range accomplishment and somewhat difficult to perform as a computer or electronics system operating function. Since triangulation usually involves two superimposed or split field images for indication it often requires the conclusion of a human interpreter to reliably complete the measurement. Another example of triangulation impracticability is to be found in the field of airborne weaponry wherein it is often difficult to locate a plurality of optical apertures at meaningful distances on an airframe,--and yet there is present a strong need for quick and accurate determination of range maps for use in rocketry and other weapons related functions.
Since many current uses for a range mapping system impose requirements of nonhuman interpretation, small physical size, the use of a single optical aperture, and accuracy in both the near field and far field environment, there is need for an improved laser imaging ranging system in the art. The system described herein responds to this need and can be conveniently referred-to by way of the acronym LIMAR/1 which is derived from the first or first and second letters of the words in the invention name.
The patent art includes several examples of range finding systems including laser operated systems which are of interest with respect to the present invention. Included in these patent examples is U.S. Pat. No. 3,409,369, issued to G. W. Bickel and concerning a laser radar system which operates on the Doppler velocity measuring principle using two different transmitted frequencies in order to obtain a conveniently low difference frequency. Since the Bickel apparatus is principally concerned with the Doppler operating concept and target velocity measurement, the present invention is readily distinguished therefrom.
Also included in these prior patents is U.S. Pat. No. 3,465,156 issued to C. J. Peters and concerned with a laser communication system which employs a narrow band noise cancellation technique with the transmitted laser beam divided into two different paths. The Peters received laser light is also split into two beams one of which contains the video signal modulation and both of which contain noise components. Since the Peters apparatus is concerned with a laser communication system, the present invention range finding concepts are readily distinguished.
Also included in these prior patents is U.S. Pat. No. 3,504,182 issued to V. F. Piezzurro et al and also concerned with an optical communication system. In the Piezzurro et al communication system scanning by the beam emitted from one station is used to "acquire" the scanning pattern of a second station in order that the two stations can lock on and be ready to transmit and receive information. Distinctions between the present invention and communications system of Piezzurro et al are readily apparent.
Also included in this art is the U.S. Pat. No. 4,515,472 of A. B. Welch which is concerned with an agile receiver for a scanning laser radar system. The Welch apparatus uses a receiver frequency adjustment arrangement in order to rapidly acquire, recognize, track and perform simultaneous guidance functions for a multiplicity of weapons against a multiplicity of targets. In view of this purpose and functioning of the Welch apparatus, distinction from the present invention range mapping system is easily discerned.